In recent years, a cancer treatment apparatus using protons or heavy ions has been developed and constructed as a radiation therapy apparatus that is intended for cancer treatment. As known well, in a particle radiation therapy that uses protons, heavy ions, or the like, it may be possible to intensively irradiate a cancer-affected area as compared to radiation therapy in the related art that uses X-rays, gamma rays, or the like, and to treat the cancer-affected region without affecting healthy cells.
A particle radiation therapy apparatus is generally provided with a rotating irradiation device (rotating gantry) in order to irradiate a patient in an arbitrary direction. The rotating gantry is adapted so as to irradiate a patient with a charged particle beam at an arbitrary rotation angle by rotating a particle beam irradiation unit through 360° of rotation.
If the rotating gantry is adapted so as to irradiate a patient with a charged particle beam at an arbitrary rotation angle by rotating a particle beam irradiation unit through 360° of rotation as described above, a treatment table to which the patient is fixed needs to be disposed on a stationary side (building) relative to the rotation and the treatment table is formed to protrude from the stationary side. Accordingly, an access floor (hereinafter, referred to as a movable floor), which is always maintained horizontal regardless of the rotation angle of the rotating gantry, is required so that a doctor, a radiation technologist, or the like, who performs the treatment, can always work while being close to the patient.
For example, FIGS. 10 and 11 show the structure of a device in the related art that is disclosed in Patent Citation 1. FIG. 10 is a cross-sectional view showing the main parts of a rotating gantry. Reference numeral 1 denotes a rotating irradiation chamber for particle radiation therapy, reference numeral 2 denotes a stationary body, reference numeral 2a denotes a guide rail of the stationary body (for a movable floor), reference numeral 2b denotes a guide rail (for a treatment bed), reference numeral 3 denotes a particle beam irradiation unit, reference numeral 4 denotes a rotating body, reference numeral 4a denotes a rotating body supporting ring, reference numeral 4b denotes a support roller, reference numeral 5 denotes a guide rail supporting body, reference numeral 5a denotes a guide rail of the rotating body (for a movable floor), reference numeral 5b denotes a guide rail supporting body supporting member, reference numeral 5c denotes supporting rollers, reference numeral 5d denotes engaging holes, reference numeral 6 denotes a movable floor, reference numeral 7 denotes rod actuating electric cylinders, and reference numeral 7a denotes locking rods. FIG. 11 is an enlarged cross-sectional view of a movable floor unit. Reference numeral 6a denotes a rubber belt, reference numeral 6b denotes a carrier, reference numeral 6c denotes a beam member, and reference numeral 6d denotes guide rollers.
The movable floor 6 includes a rubber belt 6a, a carrier 6b, a beam member 6c, and guide rollers 6d, and is formed in an endless curved shape so that the rotating gantry forms a horizontal movable floor below a treatment bed regardless of the rotation of the rotating body 4 and the particle beam irradiation unit 3. The movable floor 6 forms an access floor by being guided by the guide rail 2a of the stationary body and the guide rail 5a of the rotating body and rolling in the guide rail as the particle beam irradiation unit 3 is rotated. The guide rail supporting body 5 provided with the guide rail 5a of the rotating body is provided inside the rotating body 4 with the supporting rollers 5c interposed therebetween, and the rod actuating electric cylinders 7 for the actuating locking rods 7a are provided above the stationary body 2 provided with the stationary guide rail 2a. The locking rods 7a are formed so as to be inserted into the engaging holes 5d that are formed at the guide rail supporting body supporting member 5b for supporting the supporting rollers 5c. Accordingly, even though the rotating body 4 and the particle beam irradiation unit 3 are rotated and the movable floor 6 is moved in synchronization with the rotation of the rotating body and the particle beam irradiation unit, it may be possible to stop the guide rail supporting body 5. Therefore, it may be possible to continue to maintain the lower portion of the movable floor 6 horizontal.    Patent Citation 1: JP-A-2001-129103